Since as early as the 1600's, importance has been placed on cooling space or substances below ambient temperature. By 1930, it was discovered that when certain refrigerants underwent liquid-gas phase changes, large amounts of latent heat were absorbed and could be used to effect cooling. Today, such refrigerants are used throughout the world in annual volumes measured in the thousands of tons. Unfortunately, many of these refrigerants are now known to significantly damage the atmosphere and environment. By 1990, over fifty nations had agreed to phase out the production of chloroflorocarbons (CFC's) by the year 2000 and hydrochloroflorocarbons (HCFC's) by the year 2040. The United States has also passed statutes which, in effect, create the objective of immediately reducing emissions of these substances to the lowest achievable levels throughout the production, distribution, use and recapture for reuse, reprocessing or final disposal.
Equipment for handling these substances through production, distribution, and use have been generally available in the past simply because of the value of the product for sale at the time it enters use. However, no equipment or procedures have heretofore existed for recovering these substances without significant losses to the atmosphere. Not only must such equipment assure loss control, but it also must be cost effective and safe, but must also adapt to varieties of refrigerants, refrigeration system lubricants, and other contaminants. Furthermore, to permit reclamation and reuse of refrigerants, the reclamation equipment must prevent cross contamination of the products. Such equipment must accommodate refrigerants having various rapid phase change characteristics and must do so in a manner to permit safe normal functioning of the equipment under virtually all climatic conditions. The equipment must minimize inclusion of non-condensible gases, such as air, with the refrigerant in the ultimate storage and shipping cylinder. Further, the equipment must retain refrigerant contaminants, such as lubricants, until the reprocessing can effectively refine the refrigerants. The problem of reclamation is further complicated by the fact that the many tons of refrigerants which are to be recaptured from market use are not distributed evenly over the geographic area of use.
The U.S. Department of Transportation (DOT) has approved pressure cylinders in two sizes for refrigerant recovery and shipping. A small cylinder (see FIG. 1, hereafter described) will hold about fifty pounds of liquid refrigerant and are used by repairman to transfer used refrigerant from the refrigeration equipment to a collection point. The cylinder includes two valves, a vapor valve connected to the upper portion of the cylinder. Larger shipping cylinders (see FIG. 2 hereafter described) are capable of holding about 1000 pounds of liquid refrigerant and includes a similar arrangement of vapor and liquid valves.
At the present there are two basic means for transferring refrigerant liquids and vapors from one chamber to the other. One is commonly referred to as single direction pumping of both refrigerant liquids and vapors, and a bi-directional procedure in which only vapor is pumped, by a reversible vapor pump (see FIGS. 3a-3c hereafter described).
In the single direction pumping procedure, a liquid vapor pump is connected to the liquid valve and the liquid-vapor pump first draws liquid form the recovery cylinder and forces the liquid into the shipping cylinder. As liquid is removed from the recovery cylinder, the vapor pressure drops which in turn permits a portion of liquid in the cylinder to vaporize to maintain the vapor pressure. In other words as liquid is being removed form the cylinder, an amount remaining in the cylinder is undergoing phase change to maintain a relatively constant vapor pressure over the liquid in the cylinder. Upon completion of liquid transfer, the pump continues operating and vapors are down from the recovery cylinder in diminishing volume and compressed into the shipping cylinder where an amount converts to liquid phase. Vapor transfer from the small cylinder continues and the refrigerant vapors are eventually removed sufficiently from the recovery cylinder to prevent contaminating or mixing with the same or other types of refrigerants.
The single direction pumping of recovered refrigerant liquids and vapors has a number of problems: Non-vaporizing and heavy contaminates are concentrated in the diminishing liquid volume of the recovery cylinder. Dip tube inlets are not necessarily positioned exact to the bottom of the cylinder and the scavenging vapor flow velocity up through the tube is ever diminishing. Accordingly, an amount of contaminants such as compressor oil is likely to be retained in the recovery cylinder. Combination liquid-vapor pumps are inherently less efficient than vapor pumps because of the relation of fluid pressure, liquid versus gas viscosity and pump displacement relative to horsepower. Consequently single direction refrigerant pumping is typified by a long vapor draw-down cycle.
A number of problems are associated with current bi-directional vapor pumping systems for means of transferring recovered refrigerants. The transfer conduits fill with non-condensible air when the cylinders are disconnected and the air becomes trapped in the recovery cylinders and shipping cylinders subsequently attached. This gas is eventually transferred to the shipping cylinder and being non-condensible can prevent complete filling with liquid refrigerant. When the cylinders are disconnected from the attached conductors, the refrigerant is vented to the atmosphere. The capacity to transfer from only one recovery cylinder to the shipping cylinder is inefficient and not cost effective. There is no means for determining when all liquid refrigerant and liquid contaminants are transferred from the recovery cylinder so that the vapor pump can be reversed to begin vapor draw-down. If reversed while liquid is still in the recovery cylinder, then transferring the vapor can take longer and damage the vapor pump. The vapor pressure and accordingly vapor density at the vapor pump intake varies depending upon refrigerant temperature. If the system is designed to transfer the liquid at an efficient rate under the most unfavorable conditions, then there is a likelihood that the vapor will be heated excessively as it is pumped into the recovery cylinder. Heated vapors drawn from the recovery cylinders and transferred into the shipping cylinders progressively induce a higher level of retained vapor pressure with each transfer operation, eventually exceeding the safe operation of the system. Improperly directing the vapor pump to draw vapors when in fact liquid transfer is required can result in overfilling recovery cylinders with liquid from the shipping cylinders and can result in ingesting the liquid refrigerant into the pump. The same can occur if the shipping cylinder becomes overfilled with liquid during liquid transfer.
Pumping refrigerant vapors is a well developed art and offers a wide variety of reliable vapor pumps in various sizes. This fact coupled with limited vapor pumping capacity of combination liquid-vapor pumps potentially makes bi-directional vapor pumping the desired method for production transfer of recovered refrigerants. The present invention is of an improved Transfer System providing features necessary to fulfill regulatory demands for controlling refrigerants and further accommodating the needs of industry in processing large volumes of recovered refrigerants.